package com.dyz.leetcode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class CanFinish207 {
    //BFS
    public boolean canFinish(int numCourses, int[][] prerequisites) {
        int[]indegrees = new int[numCourses];
        List<List<Integer>> adjacency = new ArrayList<>();
        Queue<Integer> queue = new LinkedList<>();
        for (int i =0;i<numCourses; i++){
            adjacency.add(new ArrayList<>());
        }
        for(int[] cp:prerequisites){
            indegrees[cp[0]]++;
            adjacency.get(cp[1]).add(cp[0]);
        }

        for(int i=0; i<numCourses;i++){
            if(indegrees[i]==0){
                queue.add(i);
            }
        }
        //BFS
        while (!queue.isEmpty()){
            int pre = queue.poll();
            numCourses--;
            for (int cur : adjacency.get(pre)){
                indegrees[cur]--;
                if(indegrees[cur]==0){
                    queue.add(cur);
                }
            }
        }
        return numCourses==0;
    }
}
